Motor vehicles provided with chargeable electric batteries, which are in particular associated with the operation of an electric engine, have been already proposed in prior art. For example, purely electric engine vehicles are known, in which the electric engine is the only driving apparatus, as well as hybrid motor vehicles, which are equipped in addition to the electric engine also with another driving apparatus, in particular with an internal combustion engine. With the so-called plug-in hybrids as well as with electric engine vehicles, it is already known that the motor vehicle can be provided with a charging connection for connecting to a motor vehicle-external charging device, or for connecting directly to a motor vehicle-external energy system, such as for example a local network of a house, so that the battery can be charged by means of external energy sources.
Since motor vehicles are usually employed also for private use, it is desirable when the charging operation can be realized in as simple manner as possible in private use, so that the charging operations can be carried out also with a private infrastructure unit which supplies also other consumers.
Therefore, it was proposed already in prior art to provide charging devices that can be connected with a three-phase connection to the energy system of a local electric grid, and that can be provided with suitable power electronics components in order to convert the three-phase input alternating current to a current that can be used for charging a battery (direct current). Such three-phase charging devices charge the energy system evenly on all phases. Three-phase household connections or general infrastructure connection units are provided with at least one fuse for each phase, which can be impacted when it is overloaded, which is something that should be prevented by the charging device.
Various variants have already been proposed for the realization of the charging devices. So for example, charging devices that are fully integrated in the motor vehicle (On Board Chargers—OBC) are known, which are connected to the energy system with a three-phase connection via the charging connection of the motor vehicle, for example by using a motor vehicle-external wall box which can be provided with a suitable plug for the charging connection. It has also been already proposed to provide charging devices that are arranged completely outside of the motor vehicle, which are thus in particular associated with charging devices such as charging apparatuses for a particular infrastructure unit, for example direct current fast chargers, which provide a charging current that can be used directly via a charging connection of the motor vehicle for charging a battery. Moreover, other forms are also known, wherein some parts of the charging device are realized inside the motor vehicle, and some parts are realized outside the motor vehicle.
DE 10 2013 204 256 A1 relates to a charging device for an electric motor vehicle comprising a charging interface outside of the motor vehicle, to which an alternating current can be supplied at the input via a three-phase alternating current obtained from an external three-phase AC power grid, which can be supplied via a charging cable to the electric vehicle in order to charge the electric energy storage device of the motor vehicle. In this case it is proposed that the interface comprise a converter device for converting the three-phase alternating current to a one-phase alternating current for a charging current, which distributes during the operation the phase load to the line phase of a single-phase alternating current essentially in a uniform manner over the three line phases of the three-phase alternating current. In this manner, one-phase charging of electric motor vehicles can be achieved at the same time with a symmetrical load that is applied to the supply lines.
However, a problem with these and similar known charging devices is that other consumers in the infrastructure connected to different phases create an unsymmetrical load of the three-phase infrastructure unit connection. The charging device charges all of these phases, and the result may be that the line protection response causing a fuse failure may be triggered at the phase which has the highest load. If it were in this case provided that the protection of the charging device is compatible with the infrastructure unit connection and that its power is regulated and reduced in a timely manner over the three phases, the triggering of the fuse would be prevented. However, it would not be possible to exploit meaningfully the available power potential, in particular when the load on one of the phases is clearly much higher.